The present invention relates generally to the technical field of fiber optics, and, more particularly, to free-space, reflective Nxc3x97N fiber optic switches.
A dramatic increase in telecommunications during recent ears, which may be attributed largely to increasing Internet communications, has required rapid introduction and commercial adoption of innovations in fiber optic telephonic communication systems. For example, recently fiber optic telecommunication systems have been introduced and are being installed for transmitting digital telecommunications concurrently on 4, 16, 32, 64 or 128 different wavelengths of light that propagate along a single optical fiber. While multi-wavelength fiber optic telecommunications dramatically increases the bandwidth of a single optical fiber, that bandwidth increase is available only at both ends of the optical fiber, e.g. between two cities. When light transmitted into one end of the optical fiber arrives at the other end of the optical fiber, there presently does not exist a flexible, modular, compact, Nxc3x97N fiber optic switch which permits automatically forwarding light received at one end of the optical fiber onto a selected one of several different optical fibers which will carry the light onto yet other destinations.
Historically, when telecommunications were transmitted by electrical signals via pairs copper wires, at one time a human being called a telephone operator sat at a manually operated switchboard and physically connected an incoming telephone call, received on one pair of copper wires, that were attached to a plug, to another pair of copper wires, that were attached to a socket, to complete the telephone circuit. The telephone operator""s task of manually interconnecting pairs of wires from two (2) telephones to establish the telephone circuit was first replaced by an electro-mechanical device, called a crossbar switch, which automated the operator""s manual task in response to telephone dialing signals. During the past forty years, the electro-mechanical crossbar switch for electrical telecommunications has been replaced by electronic switching systems.
Presently, switches for fiber optic telephonic communications exist which perform functions for fiber optic telephonic communications analogous to or the same as the crossbar switch and electronic switching systems perform for electrical telephonic communications. However, the presently available fiber optic switches are far from ideal. That is, existing fiber optic telecommunications technology lacks a switch that performs the same function for optical telecommunications as that performed by electronic switching systems for large numbers of optical fibers.
One approach used in providing a 256xc3x97256 switch for fiber optic telecommunications first converts light received from a incoming optical fiber into an electrical signal, then transmits the electrical signal through an electronic switching network. The output signal from that electronic switching network is then used to generate a second beam of light that then passes into an output optical fiber. As those familiar with electronics and optical fiber telecommunications recognize, the preceding approach for providing a 256xc3x97256 fiber optic switch is physically very large, requires electrical circuits which process extremely high-speed electronic signals, and is very expensive.
Attempting to avoid complex electronic circuits and conversions between light and electronic signals, various proposals exist for assembling a fiber optic switch that directly couples a beam of light from one optical fiber into another optical fiber. One early attempt to provide a fiber optic switch, analogous to the electrical crossbar switch, mimics with machinery the actions of a telephone operator only with optical fibers rather than for pairs of copper wires. U.S. Pat. No. 4,886,335 entitled xe2x80x9cOptical Fiber Switch Systemxe2x80x9d that issued Dec. 12, 1989, includes a conveyor that moves ferrules attached to ends of optical fibers. The conveyer moves the ferrule to a selected adapter and plugs the ferrule into a coupler/decoupler included in the adapter. After the ferrule is plugged into the coupler/decoupler, light passes between the optical fiber carried in the ferrule and an optical fiber secured in the adapter.
U.S. Pat. No. 5,864,463 entitled xe2x80x9cMiniature 1xc3x97N Electromechanical Optical Switch And Variable Attenuatorxe2x80x9d which issued Jan. 26, 1999, (xe2x80x9cthe ""463 patentxe2x80x9d) describes another mechanical system for selectively coupling light between one optical fiber and one of a number of optical fibers. This patent discloses selectively coupling light between one optical fiber and a selected optical fiber by mechanically moving an end of one optical fiber along a linear array of ends of the other optical fibers. The 1xc3x97N switch uses a mechanical actuator to coarsely align the end of the one optical fiber to a selected one of the other optical fibers within 10 xcexcm. The 1xc3x97N switch, using light reflected back into the moving optical fiber from the immediately adjacent end of the selected optical fiber, then more precisely aligns the end of the input optical fiber to the output optical fiber. U.S. Pat. No. 5,699,463 entitled xe2x80x9cMechanical Fiber Optic Switchxe2x80x9d that issued Dec. 16, 1997, also aligns an end of one optical fiber to one of several other optical fibers assembled as a linear array, but interposes a lens between ends of the two optical fibers.
U.S. Pat. No. 5,524,153 entitled xe2x80x9cOptical Fiber Switching System And Method Of Using Samexe2x80x9d that issued Jun. 4, 1996, (xe2x80x9cthe ""153 patentxe2x80x9d) disposes two (2) optically opposed groups of optical fiber switching units adjacent to each other. Each switching unit is capable of aligning any one of its optical fibers with any one of the optical fibers of the optically opposed group of switching units. Within the switching unit, an end of each optical fiber is positioned adjacent to a beamforming lens, and is received by a two-axis piezoelectric bender. The two-axis piezoelectric bender is capable of bending the fiber so light emitted from the fiber points at a specific optical fiber in the optically opposed group of switching units. Pulsed light generated by radiation emitting devices (xe2x80x9cREDsxe2x80x9d) associated with each optical fiber pass from the fiber to the selected optical fiber in the opposing group. The pulsed light from the RED received by the selected optical fiber in the opposing group is processed to provide a signal that is fed back to the piezoelectric bender for pointing light from the optical fiber directly at the selected optical fiber.
Rather than mechanically effecting alignment of a beam of light from one optical fiber to another optical fiber either by translating or by bending one or both optical fibers, optical switches have been proposed that employ micromachined moving mirror arrays to selectively couple light emitted from an input optical fiber to an output optical fiber. Papers presented at OFC/IOOC ""99, Feb. 21-26, 1999, describe elements that could be used to fabricate s a three (3) stage fully non-blocking fiber optic switch, depicted graphically in FIG. 1. This fiber optic switch employs moving mirror arrays in which each polysilicon mirror can selectively reflect light at a 90xc2x0 angle. In this proposed fiber optic switch, rows of relatively small 32xc3x9764 optical switching arrays 52ai (i=1, 2 . . . 32) and 52bk (k=1, 2 . . . 32) receive light from or transmit light to thirty-two (32) input or output optical fibers 54an and 54bn. Thirty-two groups of sixty-four (64) optical fibers 56al,m and 56bl,m carry light between each of the 32xc3x9764 optical switching arrays 52ai and 52bk and one of sixty-four 32xc3x9732 optical switching arrays 58j (j=1, 2 . . . 64).
The complexity of the fiber optic switch illustrated in FIG. 1 is readily apparent. For example, a 1024xc3x971024 fiber optic switch assembled in accordance with that proposal requires 4096 individual optical fibers for interconnecting between the 32xc3x9764 optical switching arrays 52ai and 52bk and the 32xc3x9732 optical switching arrays 58j. Moreover, the 32xc3x9764 optical switching arrays 52ai and 52bk and 32xc3x9732 optical switching arrays 58j require a total of 196,608 micromachined mirrors.
The polysilicon mirrors proposed for the fiber optic switch illustrated in FIG. 1 are curved rather than optically flat. Furthermore, while those mirrors possess adequate thermal dissipation for switching a single 0.3 mW wavelength of light and perhaps even a few such wavelengths, they are incapable of switching even ten (10) or twenty (20) such wavelengths. However, as described above fiber optic telecommunications systems are already transmitting many more than twenty (20) wavelengths over a single optical fiber, and, if not already, will soon be transmitting hundreds of wavelengths. If instead of a single wavelength of light one optical fiber carries 300 different wavelengths of light each having a power of 0.3 mW, then 100 mW of power impinges upon the polysilicon mirror proposed for this fiber optic switch. If the polysilicon mirror reflects 98.5% of that light, the mirror must absorb substantially all of the remainder, i.e. 1.5 mW of power. Absorption of 1.5 mW of power would likely heat the thermally non-conductive polysilicon mirror to unacceptable temperatures which would further degrade mirror flatness.
U.S. Pat. No. 4,365,863 entitled xe2x80x9cOptical Switch For a Very Large Number of Channelsxe2x80x9d that issued Dec. 28, 1982, (xe2x80x9cthe ""863 patentxe2x80x9d) discloses disposing two (2) parallel arrays of optically opposed, regularly placed ends of optical fibers. The space between the two (2) arrays contains an optical switching system that includes propagation mode converters that are associated respectively with each fiber of each array. The mode converters convert light from the guided mode of propagation in glass filaments to a directive mode of propagation in free space, and vice-versa. In its simplest form, such a converter comprises essentially an optical lens whose focal point is positioned approximately at the end of the corresponding fiber.
The optical switching system of the ""863 patent also includes a light beam deflector associated with each fiber of its two arrays. Any mode converter of one array sends a beam of light to a deflector with which it is associated. The deflector receiving the light beam from the mode converter redirects the light to any one of the deflectors associated with the other array of optical fibers. The deflector receiving the beam from a deflector redirects the light to the mode converter associated with the receiving light deflector. The light beam deflectors may be of any known type. The ""863 patent specifically discloses using for light beam deflectors either a mechanical-optical device that operates on the principle of the diasporameter, or an acousto-optical deflectors based on photon-phonon interaction within a crystal medium.
Each light beam deflector in the ""863 patent is controlled by an interface control that is driven by a logic circuit. A detector is associated with each beam of light to extract from the signal carried by the beam the data corresponding to the address of the optical fiber in the respective arrays. The logic circuits are connected to a central processor which, together with these logic circuits, controls all the functions of the switching system. Each detector in the ""863 patent may, for example, include a semi-transparent mirror sampling the corresponding beam of light, an optoelectronic device for converting the sample of the beam of light into an electrical signal, and a device for decoding this electrical signal in order to extract the optical fiber address data.
A technical paper entitled xe2x80x9cA Silicon Light Modulatorxe2x80x9d by Kari Gustafsson and Bertil Hxc3x6k published in the Journal of Physics E. Scientific Instruments 21 at pages 680-85 (xe2x80x9cthe Gustafsson, et al. paper) describes an array of four, one-dimensional torsional scanners micromachined from an epitaxial layer of a silicon substrate. The Gustafsson, et al. paper describes electrostatically exciting the torsional scanners. The paper reports that operating in this way the torsional scanners have been used in a fiber-optic switch and modulator to couple light between a pair of immediately adjacent optical fibers.
The present invention provides a fiber optic switch capable of concurrently coupling incoming beams of light carried on more than 1,000 individual optical fibers to more than 1,000 outgoing optical fibers.
An object of the present invention is to provide a simpler fiber optic switch that is capable of switching among a large number of incoming and outgoing beams of light carried on optical fibers.
Another object of the present invention is to provide an efficient fiber optic switch that is capable of switching among a large number of incoming and outgoing beams of light carried on optical fibers.
Another object of the present invention is to provide a fiber optic switch which has low cross-talk between communication channels.
Another object of the present invention is to provide a fiber optic switch which has low cross-talk between communication channels during switching thereof.
Another object of the present invention is to provide an highly reliable fiber optic switch.
Another object of the present invention is to provide a fiber optic switch that does not exhibit dispersion.
Another object of the present invention is to provide a fiber optic switch that is not polarization dependent.
Another object of the present invention is to provide a fiber optic switch that is fully transparent.
Another object of the present invention is to provide a fiber optic switch that does not limit the bitrate of fiber optic telecommunications passing through the switch.
Briefly, the present invention is a fiber optic switching module adapted for use in a fiber optic switch that includes a first and a second group of optical fiber receptacles. The two groups of optical fiber receptacles are separated from each other at opposite ends of a free space optical path. Each optical fiber receptacle is adapted for receiving and fixing an end of an optical fiber. The fiber optic switching module also includes lenses one of which is fixed respectively at each of the optical fiber receptacles of the first and second groups so the end of the optical fiber fixable in that optical fiber receptacle is juxtaposed with the lens fixed thereat. Each lens is adapted for receiving a beam of light emittable from the juxtaposed end of the optical fiber and for emitting a quasi-collimated beam of light into the optical path of the fiber optic switching module.
The fiber optic switching module also includes a first and a second set of reflective light beam deflectors that are disposed in a V-shaped arrangement within the optical path between the groups of optical fiber receptacles. Each of the light beam deflectors respectively is:
1. associated with one of the lenses fixed at each of the optical fiber receptacles;
2. located so the quasi-collimated beam of light emittable from the associated lens impinges upon the light beam deflector to be reflected therefrom; and
3. energizable by drive signals supplied to the fiber optic switching module to be oriented for reflecting the quasi-collimated beam of light emittable from the associated lens to also reflect off a selected light beam deflector.
Also included in the fiber optic switching module is a mirror disposed along the optical path between the sets of light beam deflectors upon which quasi-collimated beams of light impinge.
Arranged in this way, a pair of light beam deflectors may be selected and oriented by the drive signals supplied thereto to establish an optical coupling for at least one quasi-collimated beam of light between a pair of lenses respectively fixable at any one of the optical fiber receptacles and another lens fixable at any other of the optical fiber receptacles.
These and other features, objects and advantages will be understood or apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiment as illustrated in the various drawing figures.